在JavaScript中实现堆栈和队列的最佳方法是什么?

我想做调车场算法我需要这些数据结构。


当前回答

如果有人需要它,你可以使用这个NPM包https://www.npmjs.com/package/data-structures-typescript,它有一个队列和堆栈,它支持javascript和typescript,它是通用的,所以你可以用你自己的值类型;)

其他回答

Create a pair of classes that provide the various methods that each of these data structures has (push, pop, peek, etc). Now implement the methods. If you're familiar with the concepts behind stack/queue, this should be pretty straightforward. You can implement the stack with an array, and a queue with a linked list, although there are certainly other ways to go about it. Javascript will make this easy, because it is weakly typed, so you don't even have to worry about generic types, which you'd have to do if you were implementing it in Java or C#.

如果有人需要它,你可以使用这个NPM包https://www.npmjs.com/package/data-structures-typescript,它有一个队列和堆栈,它支持javascript和typescript,它是通用的,所以你可以用你自己的值类型;)

单端队列

这是一个使用映射的队列。由于插入顺序得到了保证,所以可以像迭代数组一样迭代它。除此之外,它的思想与Queue.js非常相似。

我做了一些简单的测试,但还没有进行广泛的测试。我还添加了一些我认为很好的功能(通过数组构造)或易于实现(例如last()和first())。

它背后的简单版本/直觉如下:

class Queue {
    constructor() {
        this.offset = 0
        this.data = new Map()
    }

    enqueue(item) {
        const current = this.offset + this.length()
        this.data.set(current, item)
    }

    dequeue() {
        if (this.length() > 0) {
            this.data.delete(this.offset)
            this.offset += 1
        }
    }

    first() {
        return this.data.get(this.offset)
    }

    last() {
        return this.data.get(this.offset + this.length() - 1)
    }

    length() {
        return this.data.size
    }
}

简单版本的问题是,当内存索引超过9千万亿(Number.MAX_SAFE_INTEGER的值)时,需要重新映射内存。此外,我认为它可能很好有数组构造,它很高兴看到值正在进入队列和退出队列返回。可以通过编写以下代码来解释这一点:

class Queue {
    constructor() {
        this.offset = 0
        this.data = new Map()
        if (arguments.length === 1) this._initializeFromArray(arguments[0])
    }

    enqueue(item) {
        const current = this.offset + this.length()
        this.data.set(current, item)
        let result = this.data.get(current)
        this._remapDataIfMaxMemoryViolation(current, Number.MAX_SAFE_INTEGER)
        return result
    }

    dequeue() {
        let result = undefined
        if (this.length() > 0) {
            result = this.data.get(this.offset)
            this.data.delete(this.offset)
            this.offset += 1
        }
        if (this.length() === 0) this.offset = 0
        return result
    }

    first() {
        return this.data.get(this.offset)
    }

    last() {
        return this.data.get(this.offset + this.length() - 1)
    }

    length() {
        return this.data.size
    }

    _remapDataIfMaxMemoryViolation(current, threshhold) {
        if (current+1 === threshhold) {
            const length = this.length()
            this.offset = 0
            for (const [key, value] of this.data) {
                this.data.set(this.offset, value)
                this.data.delete(key, value)
                this.offset += 1
                if (this.offset === length) break
            }       
        }
    }

    _initializeFromArray(array) {
        for (const value of array) {
            this.data.set(this.offset, value)
            this.offset += 1
        }
    }
}

我在Chrome开发控制台进行了一些测试,对完整版本进行了以下调用。

l = console.log // I'm lazy with typing
q = new Queue()
l('enqueue', q.enqueue(1))
l('enqueue', q.enqueue(2))
l('enqueue', q.enqueue(3))
l('enqueue', q.enqueue("hello"))
l('enqueue', q.enqueue("monkey"))
l('show 5 elements: ', q.data)
l('length', q.length())
l('first', q.first())
l('last', q.last())
l('dequeue', q.dequeue())
l('dequeue', q.dequeue())
l('show 3 elements', q.data)
q._remapDataIfMaxMemoryViolation(q.length()+q.offset-1, 5)
l('show 3 remapped elements', q.data)

l(queue = new Queue([3,4,5,6,7,8,9]))
l(queue.data)

下面是一个相当简单的队列实现,有两个目标:

与array.shift()不同,您知道这个出队列方法需要常数时间(O(1))。 为了提高速度,这种方法使用的分配比链表方法少得多。

堆栈实现只共享第二个目标。

// Queue
function Queue() {
        this.q = new Array(5);
        this.first = 0;
        this.size = 0;
}
Queue.prototype.enqueue = function(a) {
        var other;
        if (this.size == this.q.length) {
                other = new Array(this.size*2);
                for (var i = 0; i < this.size; i++) {
                        other[i] = this.q[(this.first+i)%this.size];
                }
                this.first = 0;
                this.q = other;
        }
        this.q[(this.first+this.size)%this.q.length] = a;
        this.size++;
};
Queue.prototype.dequeue = function() {
        if (this.size == 0) return undefined;
        this.size--;
        var ret = this.q[this.first];
        this.first = (this.first+1)%this.q.length;
        return ret;
};
Queue.prototype.peek = function() { return this.size > 0 ? this.q[this.first] : undefined; };
Queue.prototype.isEmpty = function() { return this.size == 0; };

// Stack
function Stack() {
        this.s = new Array(5);
        this.size = 0;
}
Stack.prototype.push = function(a) {
        var other;
    if (this.size == this.s.length) {
            other = new Array(this.s.length*2);
            for (var i = 0; i < this.s.length; i++) other[i] = this.s[i];
            this.s = other;
    }
    this.s[this.size++] = a;
};
Stack.prototype.pop = function() {
        if (this.size == 0) return undefined;
        return this.s[--this.size];
};
Stack.prototype.peek = function() { return this.size > 0 ? this.s[this.size-1] : undefined; };

Javascript中的常规数组结构是一个堆栈(先入后出),也可以用作队列(先入先出),这取决于你所做的调用。

检查这个链接,看看如何让一个数组像一个队列:

队列